Methacholine challenge testing: Improved patient comfort with a 2-tiered protocol

Background: The methacholine challenge test (MCT) is a test of bronchial hyperreactivity used as an aid in the diagnosis of asthma. MCT results are reported as the provocation concentration at which the forced expiratory volume in 1 second (FEV₁) decreases 20% (PC₂₀). The requirement for a 20% or greater decrease in FEV₁ results in precipitous decreases in FEV₁ in some patients. Objective: To improve MCT safety without compromising accuracy. Methods: We performed a retrospective analysis of 879 consecutive MCTs (derivation cohort). A novel protocol for MCT was developed and validated in a cohort of 564 MCTs performed in a second institution. Results: In comparison with a PC₂₀ cutoff of less than 8 mg/mL, a provocation concentration at which the FEV₁ decreases 10% (PC₁₀) cutoff of 1 mg/mL or less has a sensitivity of 86%, a specificity of 98%, a positive predictive value (PPV) of 97%, and a negative predictive value (NPV) of 91%. We propose a novel 2-tiered protocol for MCT. If the PC₁₀ is 1 mg/mL or less, bronchial hyperreactivity is present; if the PC₁₀ is greater than 1 mg/mL, the test is continued until the provocative concentration is 8 mg/mL or a 20% decrease in FEV₁ is achieved. Compared with the standard protocol, the proposed protocol has a sensitivity, specificity, PPV, NPV, and overall accuracy of 100%, 98%, 97.6%, 100%, and 99%, respectively. The modified protocol would have enabled us to avoid 26 of 42 cases (62%) in which a 40% or greater decrease in FEV₁ occurred and would save 0.65 dose for every MCT performed. The 2-tiered protocol performed well in the validation cohort; sensitivity, specificity, PPV, NPV, and overall accuracy were 100%, 98%, 87%, 100%, and 98%, respectively. Conclusion: The proposed 2-tiered protocol is accurate, saves time, and avoids precipitous decreases in FEV₁.